Imaging systems such as printers, fax machines, and copiers are virtually omnipresent, and can be found in homes and offices worldwide. The development of such systems has facilitated improvements in communications that have in turn fostered profound changes in the ways that people live and work. Telecommuting, “virtual” offices, and intra-office networks represent but a few examples of the advancements that have been made possible by modern imaging systems.
Most imaging systems use transport mechanisms to move sheets of imaging material through the system. Typical of such arrangements are those using “nip rollers”, in which cylindrical rollers are mounted parallel to one another for rotation in opposite directions. Sheet material is gripped by the rollers in the space between the rollers, the “nip”, where rotation or the rollers causes movement of the sheet. The efficacy and reliability of material transport depends upon a variety of factors, among which are roller surface hardness and “nip spacing”, i.e., the amount of space between the roller surfaces. Optimal roller surface hardness and nip spacing varies with characteristics of the sheet material passing through the system, including sheet thickness and surface characteristics.
Known systems have taken a variety of approaches to nip roller enhancements. For example, U.S. Pat. No. 5,967,512 to Irsik is directed to a nip roller assembly for adjusting the vertical movement of a top nip roller with respect to a bottom nip roller mounted on a machine base, the assembly including a frame attached to the base, the frame including opposing upwardly extending guide legs and a datum member attached to each guide leg and extending therebetween. A support assembly is adjustably mounted on the frame. The support assembly includes a hanger member extending between the guide legs and moveably engaged with each guide leg, a pilot member attached to the hanger member and selectively adjustably attached to the datum member, a cylinder attached to the hanger member, the cylinder having a plunger which is selectively expandable and retractable from the cylinder, and a nip roller bracket for rotatably supporting the nip roller, the bracket being attached to the plunger and extending between the upright guide rods. The bracket movably engages each guide rod to allow movement of the nip roller bracket in conjunction with the rod.
U.S. Pat. No. 6,286,741 to Itoh shows a method of feeding a photosensitive material processing device, includes providing a pair of feed rollers, each in a form of a coaxially-shaped two-layer structure formed by two-layers extrusion molding using thermoplastic resin, wherein the two-layer structure of each of the feed rollers has an internal layer portion and an external layer portion wherein the modulus of elasticity of either the thermoplastic resin constituting the external layer portion or the thermoplastic resin constituting the internal layer portion of the two-layer structure is 240 kgf/mm.sup.2 or more, the modulus of elasticity of the thermoplastic resin constituting the other layer portion is 900 kgf/mm.sup.2 or more, and the external diameter of one of the feed rollers is 13.7 mm or more. The feed rollers are rotatably supported on a processing rack inside a processing tank of the device so that the rollers oppose one another, with a predetermined clearance, and the photosensitive material is directed between the feed rollers, while rotating at least one of the rollers, to convey the photosensitive material inside the processing tank.
Published U.S. patent application Ser. No. 2001/0022428 to Hebert deals with a method and apparatus for holding recording media against a media support surface of an imaging system using an arrangement of variable cross-section vacuum grooves. Each vacuum groove has a continuously decreasing cross-section along its length. Each vacuum groove has a maximum cross-section adjacent a vacuum port and a minimum cross-section at a distal end of the vacuum groove.
While known rollers attempt to address sheet adhesion and roller force, it can be seen from the foregoing that the need exists for a simple, inexpensive, roller structure that provides adjustability in nip spacing and roller force to accommodate a variety of sheet material types.